flamenco, vm: update cpi account borrowing checks

[topointon-jump]

Align CPI error checks to better reflect Agave's structure, after feedback from auditors.

• Accounts are borrowed outside UPDATE_CALLEE_ACC and UPDATE_CALLER_ACC to align better with Agave. This aligns more closely to the Agave structure.
• Errors in the borrowing are propagated. Note that this borrow should never fail unless there is a bug somewhere else in the runtime.
• Remove special-case handling of FD_ACC_MGR_ERR_UNKNOWN_ACCOUNT, as there is no reason not to error out in this case. This is a non-functional change as FD_ACC_MGR_ERR_UNKNOWN_ACCOUNT would never be thrown (all call sites return FD_EXECUTOR_INSTR_ERR_MISSING_ACC which is a different error code) but is less confusing.

[Copilot]

Pull request overview

Refactors CPI account update helpers to borrow CPI accounts at the call sites (closer to Agave’s structure) and simplifies callee/caller update code by removing in-function account lookups.

Changes:

• Changed CPI update helper signatures to accept already-borrowed accounts rather than instruction account indices/keys.
• Moved try_borrow_instr_account* calls to the call sites in CPI translation/entrypoint paths.
• Removed dead/confusing borrowing paths and key-based lookup logic.

[github-actions]

Performance Measurements ⏳

Suite	Baseline	New	Change
backtest mainnet-368528500-perf per slot	0.061455 s	0.061009 s	-0.726% ✅
backtest mainnet-368528500-perf snapshot load	3.148 s	2.386 s	-24.206% ✅
backtest mainnet-368528500-perf total elapsed	61.454603 s	61.008825 s	-0.725% ✅
firedancer mem usage with mainnet.toml	963.38 GiB	963.38 GiB	0.000% ✅

[github-actions]

Performance Measurements ⏳

Suite	Baseline	New	Change
backtest mainnet-368528500-perf per slot	0.090969 s	0.089043 s	-2.117% ✅
backtest mainnet-368528500-perf snapshot load	5.716 s	4.43 s	-22.498% ✅
backtest mainnet-368528500-perf total elapsed	90.968918 s	89.043335 s	-2.117% ✅
firedancer mem usage with mainnet.toml	963.38 GiB	963.38 GiB	0.000% ✅

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 2 comments.

[github-actions]

Performance Measurements ⏳

Suite	Baseline	New	Change
backtest mainnet-368528500-perf per slot	0.061442 s	0.060965 s	-0.776% ✅
backtest mainnet-368528500-perf snapshot load	3.224 s	2.48 s	-23.077% ✅
backtest mainnet-368528500-perf total elapsed	61.441589 s	60.964833 s	-0.776% ✅
firedancer mem usage with mainnet.toml	963.38 GiB	963.38 GiB	0.000% ✅

[github-actions]

Performance Measurements ⏳

Suite	Baseline	New	Change
backtest mainnet-368528500-perf per slot	0.061122 s	0.061069 s	-0.087% ✅
backtest mainnet-368528500-perf snapshot load	3.253 s	2.487 s	-23.547% ✅
backtest mainnet-368528500-perf total elapsed	61.12229 s	61.069424 s	-0.086% ✅
firedancer mem usage with mainnet.toml	963.38 GiB	963.38 GiB	0.000% ✅